The root and trunk of a plant of the genus Salacia have been used as a natural drug by a traditional medical science, aayurveda, in India and Sri Lanka. It has been handed down in Sri Lanka that the root skin of Salacia reticulata is effective in treating rheumatism, gonorrhea and a skin disease and is also used in the treatment of initial stage diabetes mellitus. In India, a root of Salacia oblonga is used in similar treatments, and it is said that Salacia chinensis is also used in the treatment of diabetes mellitus (FOOD Style 21, vol. 6, no. 5, pp. 72-78).
Thus, it has been handed down that plants of the genus Salacia are effective in the prevention and early stage treatment of diabetes mellitus. In recent years, it has been reported that a plant of the genus Salacia has the action to suppress increase of blood sugar value, and its action mechanism is the sugar absorption inhibitory action based on the α-glucosidase activity inhibition (FOOD Style 21, vol. 6, no. 5, pp. 72-78).
In addition, there are patents on the compounds which are contained in the extraction components of the genus Salacia and have the action to inhibit α-glucosidase activity (Japanese Patent No. 3030008, JP-A-2004-323420 and JP-A-2000-86653), and their application examples and patents as anti-diabetic agents based on the α-glucosidase activity inhibitory action (JP-A-9-301882 and Japanese Patent No. 3261090).
Since the circulating Salacia extract powder has the property to change color with the lapse of time, when the taking amount of tablets which contain the Salacia extract powder is decreased by increasing its blending amount per tablet, it exerts uneasiness and unpleasantness to consumers when ingested as food. Thus, there was a disadvantage in that the change of color must be covered by coloring it or using colored capsules.
On the other hand, when said blending amount per tablet is decreased in order to suppress the change of color, the sucrase inhibitory activity per grain becomes low (that is, the IC50 value becomes large), so that the necessary number of tablets to be ingested becomes large which imposes a burden on the ingesting persons.